Abstract
In 2011, the United Nations Road Safety Collaboration (UNRSC) developed a Global Plan for the Decade of Action for Road Safety 2011–2020. Among the categories or “pillars” of activities, is the improvement of road safety for infrastructures. Furthermore, this plan is aligned by the UN Sustainable Development Goals that included even traffic safety. In this regard, this study estimates safety improvements achieved by converting a standard roundabout into an egg turbo roundabout. In particular, turbo roundabouts have become very popular in Northern Europe for both their safety and their capacity. Many studies have shown these advantages thanks to their features: preventive separation of entering flows, limited lane changing and low speeds due to curbs. Given the absence of existing turbo roundabouts in Italy, this research studied and compared a “virtual” roundabout with spiraling circular carriageways to an existing multi-lane roundabout in order to assess its significant reduction in terms of potential collisions. This study relied on traffic conflicts in micro-simulation by using VISSIM software and then Surrogate Safety Assessment Model (SSAM). The research is based on the traffic process observed at a standard roundabout in Cosenza (Italy) marked by a high level of congestion and safety problems. Speeds, critical gaps, queue lengths, and floating car data, obtained from video observations, have been used as input data for the calibration procedure of the first scenario (case study roundabout). Then, the turbo roundabout solution was built and simulated by using the previously derived parameters. Finally, the two roundabout scenarios were compared in terms of spatial distribution of the potential conflicts determined by SSAM. The results could help to measure the performance and safety impact of these two roundabout configurations.
Highlights
In the last two decades, roundabouts have become the most common and efficient solution for at-grade intersections [1,2,3,4,5]
Starting from data acquired throughout the several recordings on the investigated roundabout, we implemented a two-step calibration procedure of VISSIM, taking into account what was reported by Gallelli et al [23]
This study analyzed the effect of turbo roundabouts on capacity, queue lengths, and potential conflicts
Summary
In the last two decades, roundabouts have become the most common and efficient solution for at-grade intersections [1,2,3,4,5]. High speeds and many potential conflicts are probably the main causes of these problems: drivers accelerate when crossing the roundabout [8,9,10,11,12] For these reasons, a new type of multi-lane roundabout, called the turbo roundabout, was introduced in the Netherlands [6] in 1996. We employed the calibrated VISSIM parameters obtained from the existing roundabout (minimizing the difference between simulated and field-observed queue lengths) to estimate the spatial distribution of the potential traffic conflicts at the virtual turbo roundabout by using Surrogate Safety Assessment Model (SSAM) [25] and to compare the results of the two different roundabout solutions
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